1. Field of the Invention
The present invention is related to a present-on-bed determination apparatus and a sleep measurement apparatus that determine whether or not a human subject is present on a bed.
2. Related Art
In recent years, a present-on-bed determination apparatus determines whether or not a human subject is present on bottom bedding such as a mattress for bed or a Japanese-style mattress (futon) has been proposed. For instance, the present-on-bed determination apparatus may be applied to a sleep measurement apparatus that measures sleeping conditions of a human subject. The sleep measurement apparatus requires an instruction by the human subject to initiate measurement of the sleeping conditions. However, there is a problem in that the human subject tends to forget to give the instruction (e.g., to operate a button) since sleep is unremarkable behavior for him or her. The present-on-bed determination apparatus enables determining whether or not the human subject is present on a bed and to execute sleep measurement without any special operation thereof by the human object. For instance, Patent Document 1 discloses a technique to determine whether or not the human subject is present on a bed (has gone to bed) by measuring body movement of the human subject (mattress oscillation) so as to measure sleeping conditions.    Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2008-206596
According to the technique of Patent Document 1, an output signal is generated from a sensor based on the mattress oscillation, and it is determined that the human subject is present on a bed if a level of the output signal exceeds a predetermined threshold. In this technique, if the mattress is subject to impact, it is likely to be determined that the human subject is present on a bed even though no one is present on the bed.